I used to play Star Wars 4th Edition Pen and Paper RPG with a 40 year old and his 32 year old wife when I was 16. They were just harmless geeks, like me.
If anything, my mom making snarky comments about the 40 year old guy really soured our relationship for a while. My friend who was my age and who also played with us sent her a picture in the mail of the 3 of us holding hands under a rainbow. She was pissed.
It’s fine. Your son could just as easily be friends with someone his age that’s a psychopath. It’s in the person, not the age. At 18 you’re going to have to trust his judgement a little more.
You don’t really know it until you stop watching videos for like a week. Suddenly you want to do your favorite things again; try things yourself again.